Until I trigger the collapse mechanism, the last comment in a post doesn’t have the number of subcomments when it hides subcomments by default. See the below pictures for an example with a specific post, but I’ve noticed this on every post I’ve seen recently.

If I reload by pulling down, it again hides the comment number.

Without the comment number after loading the post: Without the comment number

After tapping to collapse the comment, comment count shows: After tapping